The present invention relates to improved apparatus for use in assembling lumber, together with special fastener plates, to make trusses and girders in a wide variety of sizes and designs.
Wooden trusses and girders for use as structural members of buildings are commonly assembled of dimension lumber cut to proper lengths and held together by specially designed fastener plates which include multiple prongs which protrude into the lumber. Efficient manufacture of such trusses and girders requires the ability to cut, align, and fasten pieces of lumber both quickly and accurately. While such trusses and the like can be assembled manually, a jig is usually required in order to produce them efficiently. In the past, for this reason, trusses have usually been built in large numbers in factories, using jigs and stationary pressing equipment.
There are, however, several disadvantages to construction of trusses in factories. A principal disadvantage is the additional cost of transportation of assembled trusses, compared with the cost of transporting lumber, since assembled trusses take up a much greater amount of space. If therefore requires a larger number of trucks and a larger amount of fuel to transport them. Additionally, transportation of already-assembled trusses removes the opportunity for quality control during their assembly from the contractor who will ultimately be responsible for the quality of the building constructed using such trusses.
Another disadvantage of factory assembly of trusses is that the overhead expenses involved with construction of trusses at a factory, rather than at a construction site, are significant, since a factory building and the land on which it stands must be maintained and will be taxed, and the initial cost of installation of the machinery normally used in truss manufacture in the past is quite expensive. Profitability of a factory installation depends on the end market for assembled trusses being close enough to the factory that economies of production scale will absorb transportation costs.
Yet another disadvantage of factory construction of trusses is the amount of lead time required to ensure that assembled trusses can be delivered when required to avoid construction delays for lack of materials.
Because of the disadvantages of factory construction of trusses, portable equipment has been developed to manufacture trusses. The need to be able to quickly locate pieces and connect them to one another to make several identical trusses accurately and quickly must be combined in such machines with the ability to modify the jig arrangement to provide for assembling trusses of different designs and sizes conveniently. In particular, McDonald U.S. Pat. Nos. 4,174,061 and 4,304,046 disclose portable apparatus for fabricating wooden trusses. Apparatus of this general type previously available has typically used a press suspended from a boom to set fastener plates to join together the parts of a truss by pressing them into the wooden truss members. Such presses have typically been of the C-clamp type, or of the scissors type disclosed in McDonald U.S. Pat. No. 4,262,588. While such presses are capable of assembling roof trusses, they do not always have a deep enough reach for assembly of floor girders where the lumber pieces are assembled in a different orientation requiring fasteners to be set in the more widely separated edges of the lumber.
Because the presses which have been previously used include a pair of opposing jaws and a motor to force the jaws together to set fastener plates into wooden truss members the suspended weight of such presses is quite substantial. The amount of the weight causes several problems, making it desirable to have available a lighter press. The weight of a heavy press limits the span or increases the weight of booms to support it. Limited boom span limits the size of trusses which can be assembled using apparatus including such a heavy press. A heavier press also requires more force or time to move it from position to position for use in assembling trusses.
There is also a risk of unintentionally crushing one's hands, or damaging the press or boom by inappropriately using a press which is complete in itself.
A requirement exists, then, in view of the previously available apparatus for assembling wooden trusses, for a truss-assembling apparatus capable of easily being adjusted to assemble trusses of a wide variety of sizes and designs including floor girders as well as roof trusses, and including a press of adequate capacity but of lighter weight and improved safety in comparison with previously available presses for this purpose. Such apparatus should preferably be self-contained and sufficiently portable to permit its use at a construction site, rather than requiring a central factory location for assembly of trusses.